It is known to equip a flight control device with a force sensing device, the latter being designed to apply forces on the flight control device, so as to produce a sensation for the pilot.
A first known type of force sensing device, which can be described as “force-feedback device”, is designed to apply, on the flight control device, forces connected to actual phenomena acting on the device being piloted by the control device. For example, forces applied on a control surface of the wing can lead to the production of torque on the control member of that wing, using the force-feedback device.
A second known type of force sensing device, which can be described as “artificial sensing device”, is designed to apply, on the flight control device, forces not directly connected to phenomena acting on the aircraft. For example, an artificial sensing device can simply apply a force sensing torque on the flight control device, in particular to compensate for an oscillating torque phenomenon between the aircraft and the pilot (also called pilot-induced oscillations, or PIO). It is also possible to provide an artificial sensing device that is able to apply an artificial vibration, or a notching sensation, when the control device is moved, in order to inform the pilot that a particular event has occurred during piloting of the aircraft.
To generate the forces producing the sensations for the pilot via the flight control member, these force sensing devices comprise a rotating device for generating the sensation. The rotating device can be active, such as a four-quadrant motor; semi-active, such as a magnetic-rheological powder device; or passive, such as a generator, a nonpowered brushless motor, or a hydraulic rotary shock absorber.
In light of the significant forces required to provide a sensation perceptible by the pilot, the flight control member is mechanically connected to the rotary device generating the sensation via a mechanical reducing gear. Based on the application, the mechanical reducing gear has a reduction ratio comprised between 50 and 200. If a shock absorber is simulated, the shock absorption coefficient produced by the rotary device on the pilot's control member is multiplied by a factor comprised between 2500 and 40,000, for this reduction ratio range.
The application of such a mechanical reduction to an aircraft flight control device requires the mechanical reducing gear to generate particularly low friction, while having a particularly high efficiency. Furthermore, it is necessary for the play to be as small as possible, optionally zero, in order to guarantee appropriate precision and piloting comfort. Furthermore, it is necessary for the control to be gentle; i.e., for the friction and the efficiency to be constant and free of any undulation over the entire travel of the control device. These requirements must be satisfied for a relatively broad operating temperature range, for example between −40° C. (degrees Celsius) and 60° C. Indeed, the range relative to flight control devices is singularly demanding, not only due to the relative constraints of the aeronautics field, but also because it is necessary to ensure perfect control ergonomics for the pilot, who acts with great precision and sensitivity on the flight controls. The pilot will experience any defect existing within the mechanical reducing gear very quickly, where such a reducing gear could have been perfectly appropriate for other applications.
In the known devices, the mechanical reducing gear is generally made up of a gear train, which generally does not make it possible to meet all of the aforementioned requirements, some of which are antagonistic, namely the absence of friction and the absence of play.